I am trying to position a number of objects under program control, each in its own Display icon, using the Effects-in area dialog. I want to be able to move several objects but keep them positioned exactly with respect to each other. This seems
difficult at best. I think I have grasped the "in area" option on the effects
dialog, and setting up the area rectangle and variables. What throws me
is the Base and End position values. This is confusing. What is
the most straightforward way to set the position of an object in direct screen
coordinates, i.e. move a box to 100,100 or 200,100?

If you're using a version before 4.0:
Assuming you are using a 640 by 480 screen, if you really want to do this, you'll
need to set the base to 1 and the end to 640. Position the base so the
line defining the area is straddling the edge of the screen. You may have to
play with this to get it precise. Remember, it's the center of the object
that gets placed.

If you're using version 4.0 or later:
In version 4.0 and later, this becomes much easier. Macromedia heard your
cries for being able to center objects according to pixel coordinates in addition
to being able to do it according to a coordinate system of your choosing.
To use pixel coordinates, use the "On Screen" option in the Properties dialog
box. The following dialog box is set up to show the picture smack in the
middle of the Presentation Window.